Window parent = SwingUtilities.getWindowAncestor(comp);
JDialog dialog = new JDialog(parent);
dialog.setTitle(title);
dialog.setModal(true);
dialog.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
dialog.setContentPane(new HelpPanel(url));
dialog.pack();
dialog.setMinimumSize(dialog.getSize());
dialog.setLocationRelativeTo(parent);
dialog.setVisible(true);
}